Hydroconversion of coal with combination of catalysts



R. HODGSON 3,532,617

HYDROCONVERSION OF COAL WITH COMBINATION OF CATALYSTS Oct. 6, 1970 FiledJuly 23, 1968 INVENTOR R- L- HODGSON BY:

#MJM

HIS ATTORNEY United States Patent 3,532,617 HYDROCONVERSION OF COAL WITHCOMBINATION OF CATALYSTS Russell L. Hodgson, Lafayette, Calif., assignorto Shell Oil Company, New York, N.Y., a corporation of Delaware FiledJuly 23, 1968, Ser. No. 746,820 Int. Cl. Cg l/06, 1/08 U.S. Cl. 20810 7Claims ABSTRACT OF THE DISCLOSURE A process for hydroconversion of coalto refinable liquid products in which the coal is hydrogenated in thepresence of at least two catalysts, one being impregnated on the coal,to obtain both increased conversion and improved selectivity to gasolineand gas oil components.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the hydroconversion of coal to liquid products. Moreparticularly it relates to a process for hydrogenation of coal whereincoal is impregnated with a catalyst to enhance conversion and theimpregnated coal is contacted with a heterogeneous catalyst in thepresence of hydrogen to improve product selectivity.

Description of the prior art A practical process for converting coal toliquid fuels as a means of utilizing the extensive energy reserves inthe worlds coal deposits has been a much sought after goal since it wasfirst demonstrated nearly 60 years ago that coal could be hydrogenatedto liquid products. Particularly large research efforts were carried outin Germany prior to and during World War II and in the United States bythe Bureau of Mines following the war. The number of publications andpatents in this area is astronomical, as witnessed by a Bureau of Minesbibliography compiled at the outset of their efforts in the late 1940scontaining over 6,000 entries. [1. L. Wiley and H. C. Anderson, BureauMines Bull. 485: Part I (1950); Part II 1951); Part III (1952)]. Work oncoal hydrogenation has not waned in recent years; in fact, it isapproaching fruition in the form of economical processes for convertingcoal into refinable liquid products.

Several unique problems associated with the conversion of coal torefinable liquid products result from its chemical and physical nature.Not only is the starting raw material a solid, but even when completeconversion of the organic matter'is obtained, an appreciable amount ofinorganic ash remains. The condensed nature of the coal molecule resultsin a low hydrogen/ carbon ratio, necessitating the addition of largeamounts of hydrogen.

In general, processes developed for conversion of coals into liquidproducts require that the coal be first broken down to a liquid statewhich can be processed further by more or less conventional petroleumrefining techniques such as hydrofining, hydrocracking, reforming, etc.While the first step may be merely a thermal treatment, there aresignificant advantages for catalytic hydrogenative decomposition orliquefication. However, the most effective means known require very highpressures in the range of 2000 to 6000 p.s.i.

In recent years several schemes have been undergoing rather extensivedevelopment to obtain commercially feasible processes. Basically, threerather different schemes are employed. In one, coal is extracted with asolvent to remove ash and residue, the extract hydrogenated and theresidue and char coked or carbonized. Eln another, lique- 3,532,617Patented Oct. 6, 1970 'ice fication is accomplished by successivelyhigher temperature stages of pyrolysis or thermal decomposition. In thethird the coal is subjected to hydrogenation in a reaction zone whereina particulate hydrogenation catalyst is maintained in an ebullating bed.Exemplary of the various publications describing these developments isChemical and Engineering News, June 12, 1967, pp. 96-100.

One major drawback of all the proposed processes is the relatively largeamount of refractory residues and coke which are produced. Thesefractions are usually further treated by coking (or carbonization)and/or extensive recycle to the hydrogenation zone.

Obviously any proposal which reduces production of residue and coke (orchar), especially when accompanied by increased production of lowerboiling refinable products is of a major significance.

The present invention is such a process, accomplishing a high degree ofconversion and greatly improved selectivity to gasoline and gas oilboiling range products. This is accomplished by the use of a combinationof at least two catalysts; one being intimately dispersed or impregnatedon the coal and the other a heterogeneous catalyst. The dispersedcatalyst increases conversion and speeds hydrogenation while the secondacts primarily to improve product selectivity and product boiling rangedistribution.

SUMMARY OF THE INVENTION In broad aspect, the invention is a process forhydroconversion of coal using a combination of at least two catalysts;one of which is impregnated on the coal, the other contacted with theimpregnated coal in the presence of hydrogen at elevated temperature andpressure. One catalyst which is impregnated on the coal or intimatelydispersed thereon, increases initial breakdown of the com plex coalstructure; the second catalyst eifects and improves product selectivityto distillate (as opposed to residual) products.

The process of the invention may be carried out for the hydrogenation ofany type of coal, as for example, bituminous, sub-bituminous or lignitecoal. The coal should desirably be ground or pulverized to increase theefliciency of catalyst contacting.

According to the invention, coal is first impregnated with a catalyst,the impregnate solvent or vehicle optionally removed and the resultingcatalyst-impregnated coal contacted with a second particualtehydrogenation catalyst (preferably a hydrogenation metal or metalcompound supported on a solid carrier) in the presence of hydrogen atelevated temperature and pressure.

In the first step, e.g., catalyst impregnation, coal is slurried with acatalyst which is dissolved or dispersed in a liquid vehicle. Thusefficient dispersion of the catalysts. necessarily used in smallamounts, with the coal is accomplished.

Catalysts which are elfective include metal compounds, particularlymetal halides and metal sulfides. Another class of catalysts are metalnaphthenates. Naphthenates have the advantage of being soluble inhydrocarbons allowing the use of a hydrocarbon or organic impregnationvehicle and thus better contact and dispersion.

Especially preferred are catalysts which are prepared in situ on thecoal. For example, metal naphthenates are dispersed on the coal byimpregnation of the coal with either a metal salt or a naphthenic acidfollowed by conversion to the metal naphthenate. Another class of insitu prepared catalysts are metal sulfides which are dispersed on thecoal by impregnation of coal with a metal salt followed by gaseoussulfiding to the metal sulfide. The method of in situ catalystspreparation and its advantages are included in my copending patentapplication Ser. No. 686,345, filed Nov. 28, 1967, the pertinentdisclosure of 3 which is hereby made a part of and incorporated intothis application.

In many cases, for example, when the first catalyst is impregnated froman aqueous solution, it will -be highly desirable to remove the solvent,e.g., by evaporation or drying.

The particulate catalyst of the invention is a hydrogenation catalyst,preferably a catalyst composite comprising a hydrogenation metal ormetal compound (oxide or sulfide) on a solid support. The preparation ofsuch catalysts is well known in the art. Suitable hydrogenationcomponents include metals, metal oxide and sulfides, especially metalsof Group VI and Group VIII of the Periodic Table of the Elements, theircompounds and mixtures thereof.

Particularly suitable solid carriers are refractory oxides, for example,silica, alumina, zirconia, magnesia, etc. or mixtures thereof. Ingeneral, carriers having high intrinsic acid cracking activity are notrequired although some acidic cracking function is desirable, the degreeof cracking ability is dependent inter alia upon the desired conversionselectivity between low and high boiling products. Crystallinealumino-silicates are also desirable and effective catalyst carriers andin some cases are particularly effective as will be discussed more fullybelow. Faujasites, particularly synthetic Y-faujasite, are especiallypreferred crystalline alumino-silicate catalyst supports. Exemplary ofsuitable catalysts which have been found to accomplish the advantages ofthe invention are cobalt/molybdenum on alumina and palladium onY-faujasite aluminosilicates.

It will be understood that the metal component of both the impregnatedcatalyst and the particulate catalyst may, in some instances, be thesame. However, it is well recognized that the chemical form, as well asthe physical form of metal and metal compound catalysts, are highlysignificant factors in catalytic performance. Thus, the reference hereinand in the claims to two catalysts are not intended to exclude catalystscontaining the same metal component.

In the process of the invention, hydrogenation with the combination ofcatalyst is carried out at temperatures in the range of 200-600" C. andhydrogen pressures from about 500-3000 p.s.i.g. One significantadvantage of the invention is, in fact, the ability to effect high coalconversion at pressures which are lower than required in previouslyproposed processes. Pressures in the range of 2500-5000 p.s.i.g. aregenerally required with known processes.

Hydrogenation can be carried out, of course, over a wide range ofconditions depending upon the catalysts used, the type of coal beingprocessed and the desired degree of conversion.

In one embodiment of the invention, hydrogenation of impregnated coal iscarried out in the presence of particulate catalyst maintained in randommotion within a reaction zone by upfiowing recycle liquid, hydrogen and/or other gases. Suitable for this purpose is a reaction system with anebullating catalyst bed as described in Johanson, U.S. Re. 25,770,issued April 1965.

Unlike other coal hydrogenation processes based on the use of anebullating bed hydrogenation zone, the present invention involves theuse of at least two catalysts which result in greatly improved productconversion and selectivity to nonresidual products. Moreover, theprocess is operable at lower pressures than previously proposedprocesses.

DESCRIPTION OF THE DRAWING AND PREFERRED EMBODIMENT The invention willbe more completely understood by reference to the accompanying drawingwhich is a diagrammatic representation of a preferred embodiment of theinvention.

Coal enters the process via line 11 to a crusher pulverizer 1 where itis reduced in size for efficient impregnation. The crushed coal istransferred to an impregnation vessel 2 where it is mixed with acatalyst such as, for example, ammonium molybdate, in aqueous solution.The catalyst slurry or solution is introduced via line 21. Sullicientsolution is added to give the desired amount of catalyst on the coal.

Any hydrogenation metal salt which can be converted to metal sulfidesand/or naphthenates are suitable for the practice of the invention.Nickel, tin, molybdenum, cobalt, iron and vanadium salts are especiallypreferred.

Any suitable solvent may be used as a carrier for the impregnate, waterbeing of course a logical choice in many instances. However, a lowerboiling solvent which can be easily recovered is desirable in someapplications. The requirements are solubility of the impregnate in thesolvent and nonreactivity or at least limited reactivity of the solventwith the coal. For example, ether has proved a particularly suitablesolvent for impregnation of such salts as molybdenum chloride. Theconcentration of the impregnate in the solvent is not critical. Itshould be as high as possible to minimize solvent requirements andrecovery but not so high as to impair the dispersion or to render thephysical properties of the solution unmanageable. Use of appropriateconcentrations within these broad limits is within the skill of those inthe art.

When a metal salt catalyst is used, the amount should be in the range ofabout 0.01 to 5.0% by weight; an amount between 0.05 and about 1.0%weight being preferred.

From the impregnation step the coal and impregnating solution istransferred via line 13 to a drying vessel 3 where solvent is removed.This may be done in various ways well known in the art, as for example,by passing a hot inert gas through a fluidized bed of coal. Solvent isremoved via line 31 and the coal containing the intimately mixedcatalytic metal or salt passes via line 14 to vessel 4 where the metalsalt is converted to the catalytically active form. Sulfiding isoptional but is preferred for use with many metal catalysts used in thepresent invention. The advantages of sulfiding to convert the catalystmetal to an active metal compound or to a sulfided form are morecompletely outlined in my copending application, Ser. No. 686,345, filedNov. 28, 1967.

When the catalyst is converted, in situ, to the sulfide, any sulfurcompound which gives the sulfide compound, i.e., which reacts with theimpregnated metal salt is suitable. Hydrogen sulfide is preferred.Again, concentration is not critical and any available hydrogensulfide-containing gas may be used as, for example, hydrogen sulfideoff-gas from refinery streams is appropriate. Relatively pure hydrogensulfide may, of course, be used. Elevated temperatures are desirable forsulfiding, for example, temperatures in the range of 2 0O-500 C. Ingeneral, suflicient sulfur should be added to convert substantially allthe metal to the sulfide form.

Sulfur compound gas enters the sulfiding reactor through line 22. Fromunit 4, if sulfiding is used, or vessel 3 if sulfiding is not practiced,the impregnated coal enters a hydrogenation zone 5 via line 15. In thehydrogenation zone it is preferred that an ebullating bed ofheterogeneous catalyst be used as explained hereinbefore.Hydrogen-containing gas enters the zone via line 34, gaseous productsleave the zone via line 36 and liquid product, suspended char and ashand catalyst fines, if any, are removed via line 16.

In the hydrogenation zone, temperatures in the range of 350450 C. andhydrogen pressures in the range of 1000-2000 p.s.i. are preferredconditions which allow maximum advantage to be taken of the dualcatalyst system. Of course, higher temperatures and/ or pressures may beused if desired. Gaseous products and any excess hydrogen and/ or gasesused in the hydrogenation zone are removed via line 36 where they passto separator 7. Hydrogen gas which is separated in separator 7 may berecycled via line 32, mixed with incoming fresh hydrogenation gas fromline 23 and returned to the hydrogenation zone 5. Recycle ofhydrogenation gas is optional and should not be practiced if the productgas contains excessive poisons which would reduce the effectivepracticeand to point up the advantages of the present invention.

EXAMPLE I A series of experiments were made on thehydrogenation-liquefaction of Illinois No. 6 coal. Representative nessof the hydrogenative catalysts in the hydrogenation analysis of thiscoal is shown in Table L zone. Of course, where undesirable componentsare prescut, the gas may be purified before recycling. Table I Freshhydrogenation gas, preferably a concentrated hydrogen stream, enters thesystem via line 23. It is not gii i (percentw') nhnols 6 $2 necessary toemploy pure hydrogen-containing gas such H dro as off-gases from e.g.,the catalytic reforming of naphy g Nitrogen 1.5 thas belng suitable andexpedient. Other hydrogen-con- Sulfur 4 3 taining gases from processeswhich produce hydrogen OX en from hydrocarbons are also suitable. yg TH/C (atomic ratlo) 0.8 In an ebullatlng bed reaction system, asubstantial MOlSlZUIC (percent w.) 10.9 portion of the converted coal 1sremoved as a liquid via Ash ercent w 13 3 line 16. In the presentinvention, this stream will be p somewhat lower boiling than inpreviously proposed lAmlysls on mmstule and ash-free (MAP) basisschemesdue to the increased gasoline make resulting The use of combinations ofcatalysts was examined from the use of two catalysts. The liquidfraction will using powdered palladium on Y-zeolite catalyst (obtainedcontain not only converted coal, but also ash, char, and from LindeCompany and designated as SK100) lmixed a minor amount of catalystfines. One advantage of the with powdered, impregnated Illinois No. 6coal. The ebullating bed operation is the attrition of catalyst whichmixed solids were treated with a 200 cc./min. flow of tends to keepfresh catalyst surface available. This mixed hydrogen at 1500 p.s.i for5 hours at 425 C. The results stream passes via line 16 to separationzone 6 where distilare summarized in Table II. For comparison purposes,lable oil is taken overhead as the major product. This frac- SiO whichhas no catalytic hydrogenation activity was tion, which containsprimarily gasoline and gas oil boiling used instead of the zeolite withuntreated raw coal, sulrange liquids, may be further refined byconventional pefided coal, and molybdenum impregnated and sulfidedtroleum refining means. The residue is discharged via coal. Sulfidingthe coal had little effect in the absence of line 35. The residuecontains unconverted coal, if any, an impregnated catalyst. Impregnatingwith -0.1%- tar, heavy residual liquids, and ash which was introduced0.2% w. molybdenum and then sulfiding increased both with the coal, andthe impregnated catalyst. The tar, heavy conversions and yield of liquidproducts. The use of palresidual liquids and unconverted coal can beseparated ladium on Y-zeolite in place of the Si0 did not aflfect fromthe ash and if desired recycled via line 37 to hythe conversionappreciably but did alter the distribution drogenation zone 5.Alternatively, it may be used to imof products so that almost all therecovered products pregnate fresh coal with catalyst contained in aresidual boiled below about 200 C. With palladium on Y-zeolite stream oras a parting liquid from the impregnated coal. as the heterogeneouscatalyst, sul-fiding the coal or im- The quantity of this material isless with the present inpregnating with molybydenum increased conversionwhile vention than in known processes. The hydrocarbon resi- 40 stillgiving good product selectivity. When the coal was due can be coked torecover additional refinable prodimpregnated with molybdenum, sulfided,and then used nets and coke, or total hydrocarbon residue or chargasiwith palladium on Y-zeolite, the best results were ob fied toproduce hydrogen. Recovery and reuse of catalysts tained: 57% w. basismoistureand ash-free coal (MAP) will depend upon the total economics ofthe particular liquid product in the gasoline range (C -200 C.) at asystem. If small quantities of inexpensive catalyst are coal conversionof -85% w. (MAP). In these experiments, used, recovery may not bejustified. Catalyst reuse is not the molybdenum was impregnated to alevel of -01- considered a vital part of the present invention, but the0.2% w. from an ether solution of MoCl Similar impossibility of reuse insome cases is a definite advantage. pregnation to -0.0l% w. Mo was lesseflective; however, For example, catalyst contained in the recycleresidual impregnation with aqueous ammonium molybdate at liquid may beused to impregnate fresh coal. 0.6% w. Mo was equally effective. Nickelchloride im- The process scheme described is an efficient means ofpregnated and sulfided was also effective when used with utilizing thepresent invention and a preferred embodithe palladium on Y-zeoliteheterogeneous catalyst.

TABLE II Products (percent w. MAF) Conversion Heterogeneous C4- 200-(percent w. catalyst n Coal treatment b 200 0. 400 C. Char MAF) SiO None14 23 33 67 Si02 Su ed. 15 26 33 2 S102" MoClr, (I) (S) 22 37 22 78 Pd/Yone 31 0 41 59 Pd/Y sulfided.-. 44 1 27 73 Pd/Y- M0015 d (I) 46 7 9 91Pd/Y. M0Cl5 d (I) (S) 57 3 14 86 Pd/Y M0015 (I) 45 4 22 7g Pd/Y (NH46M07024 (1) (S). 57 1 15 Pd/Y NiCLz B (I) (S) 45 11 15 85 Caleined andsulfided (-10 g.) mesh), SiOz not calcined or sulfided. Illinois N0. 6(-10 g.) (100-200 mesh), (I) Impregnated; (S) Sulfided. Materialrecovered from 200 0. lines and traps.

8 -0.01% w. Mo.

1 -0.6% w. Mo. 8 -0.5% w. Ni.

ment, but is not to be considered a limitation thereon. Many variationswithin the scope of the invention which may be employed to improve theoperation in any particular system will occur to those in the art.

EXAMPLE II Another set of experiments were made using a particulatecatalyst consisting of cobalt and molybdenum impregnated on alumina, aknown catalyst for petroleum The following examples further serve toillustrate the 75 refining and available commercially. The results aresummarized in Table III. Compared to SiO which like alumina has nocatalytic hydrogenation activity, the Co/Mo/ A1 shows increasedconversion and yields with raW coal, sulfided coal andmolybdenum-impregnated and sul fided coal. The Co/Mo/Al O functions toimprove the product distribution. Impregnated FeSO also showed goodactivity with Co/Mo/Al O TABLE III.DOWNFLOW TUBE REACTOR Hz-200 ccJmin.for 5 hrs. at 1,500 p.s.i.

Products (percent w. MAF) selected from a group consisting of metals ofGroup VI and Group VIII of the Periodic Table of Elements, and compoundsand mixtures thereof and the refractory oxide support is selected from agroup consisting of silica, alumina, zirconia, magnesia and mixturesthereof.

3. The process of claim 1 wherein the refractory oxide is a crystallinealumino-silicate.

a Calcined and sulfided (-10 g.) 100 mesh). SiOz not calcined orSulfidcd.

b Illinios No. 6 (-10 g.) (100-200 mesh).

0 Material recovered from 200 0. lines and traps.

The most striking feature of the results of the experiments outlined inExamples I and II is the greatly improved selectivity of the dualcatalyst system. In all experiments carried out according to the methodof the invention, the char or residue is significantly reduced andgasoline and gas oil product significantly increased. This improvementnot only directly enhances the feasibility of coal conversion to usablepetroleum products but greatly reduces the problems associated with theresidue treating and/or disposal necessitated by the processesheretofore proposed.

I claim as my invention:

1. A process for hydroconversion of coal to liquid products boiling inthe gasoline and gas oil range comprising impregnating coal with a firstcatalyst selected from halide, sulfide, or naphthenate of a metal havingcatalytic activity to promote hydrogenation, and contacting thecatalyst-impregnated coal with a second catalyst of a hydrogenativemetal component supported on a refractory oxide support having acidcracking activity at a temperature from ZOO-600 C. and under a hydrogenpressure of from 5003000 p.s.i.g.

2. The process of claim 1 wherein the hydrogenative metal component ofthe second particulate catalyst is 4. The process of claim 1 wherein thefirst impregnated catalyst is prepared by forming the catalytic compoundin situ on the coal by impregnating one component of the catalyticcomponent on the coal followed by reacting the component to the desiredcatalytic species.

5. The process of claim 1 wherein the impregnated coal and particulatecatalyst are contacted in a reaction zone wherein the particulatecatalyst is an ebullating catalyst bed.

6. The process of claim 1 wherein the impregnated catalyst is used in anamount in a range of between 0.01 to 5.0% W. basis impregnated coal.

7. The process of claim 1 wherein the impregnated catalyst is recoveredand used to impregnate fresh coal feed to the process.

References Cited UNITED STATES PATENTS 2,377,728 7/1969 Thomas 208-10PAUL M. COUGHLAN, 111., Primary Examiner V. OKEEFE, Assistant Examiner

